Paper 4 States of Matter Structured Practice
4 structured exam questions on states of matter for IGCSE Chemistry Paper 4. Covers kinetic particle theory, changes of state, heating curves, and diffusion experiments. Total: 25 marks.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Four structured questions in the style of IGCSE Chemistry Paper 4, totalling 25 marks. Write your answers in full before checking the mark scheme.
Question 1 (7 marks)
The diagram shows the heating curve of a pure substance heated at a constant rate from -20 degC to 120 degC.
The curve shows two flat sections: one at 0 degC and one at 100 degC.
(a) Name the change of state occurring at 0 degC. [1]
(b) Explain, in terms of particles and energy, why the temperature remains constant at 100 degC even though heating continues. [3]
(c) Describe the arrangement and movement of the particles at 50 degC. [2]
(d) State whether the change from solid to liquid is exothermic or endothermic. Justify your answer. [1]
Mark scheme
(a) Melting [1]
(b) The energy supplied is used to overcome/break the intermolecular forces / attractive forces between particles [1]. The energy increases the potential energy of the particles, not their kinetic energy [1]. All the energy goes into separating the particles, so the temperature does not rise until all the liquid has become gas [1].
(c) Particles are close together but not in a fixed/regular arrangement [1]. They move randomly, sliding past each other [1].
(d) Endothermic --- energy must be absorbed to overcome the forces holding the particles in the solid structure [1].
Total: 7 marks
Question 2 (6 marks)
Cotton wool soaked in concentrated ammonia solution (Mr = 17) is placed at one end of a horizontal glass tube. Cotton wool soaked in concentrated hydrochloric acid (Mr = 36.5) is placed at the other end. After several minutes, a white ring of ammonium chloride forms inside the tube closer to the hydrochloric acid end.
(a) Write the equation for the reaction that produces the white ring. [1]
(b) Explain why the white ring forms closer to the hydrochloric acid end. [3]
(c) Predict how the time taken for the ring to appear would change if the experiment were repeated at a higher temperature. Explain your answer. [2]
Mark scheme
(a) NH₃(g) + HCl(g) → NH₄Cl(s) [1]
(b) Ammonia has a lower relative molecular mass (Mr = 17) than hydrogen chloride (Mr = 36.5) [1]. Lighter molecules move / diffuse faster [1]. Ammonia particles therefore travel further along the tube in the same time, so the ring forms closer to the HCl end [1].
(c) The ring would form in a shorter time / faster [1]. At a higher temperature, particles have more kinetic energy and move faster, so both gases diffuse more quickly [1].
Total: 6 marks
Question 3 (6 marks)
A student investigates diffusion by adding a crystal of potassium manganate(VII) to water at three different temperatures: 10 degC, 25 degC, and 60 degC. The time taken for the colour to spread uniformly is recorded.
(a) Define diffusion. [2]
(b) Predict and explain how the time changes as the temperature increases. [2]
(c) Explain why diffusion in liquids is slower than diffusion in gases, in terms of particle theory. [2]
Mark scheme
(a) The net movement of particles from a region of higher concentration to a region of lower concentration [1], as a result of their random motion [1].
(b) The time decreases / diffusion is faster at higher temperature [1]. At higher temperature, particles have more kinetic energy and move faster, so the net movement from high to low concentration occurs more quickly [1].
(c) In liquids, particles are close together, so a diffusing particle makes frequent collisions and its progress is slowed [1]. In gases, particles are far apart with large spaces between them, so there are fewer collisions and the particle moves further between collisions [1].
Total: 6 marks
Question 4 (6 marks)
A student heats solid naphthalene in a boiling tube and records its temperature every minute. The results are plotted as a heating curve.
(a) Describe what happens to the temperature during the change of state from solid to liquid. [1]
(b) Use kinetic particle theory to explain why a gas occupies a much larger volume than the same mass of liquid. [3]
(c) Explain why evaporation causes the temperature of the remaining liquid to decrease. [2]
Mark scheme
(a) The temperature remains constant during melting [1].
(b) In a gas, particles have enough kinetic energy to completely overcome the intermolecular forces [1]. They are far apart with large distances between them / no fixed arrangement [1]. They move rapidly in all directions, spreading out to fill the available space/volume of the container [1].
(c) During evaporation, the particles with the highest kinetic energy escape from the surface of the liquid [1]. The remaining particles have a lower average kinetic energy, so the temperature of the liquid decreases [1].
Total: 6 marks
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